Self-regulating blood pump

ABSTRACT

A self-regulating peristaltic pump having a pumping chamber of enhanced operating life. The operating life of the tubing is improved by a combination of features including providing the tubing with a naturally collapsed passageway. The tubing is collapsed when the internal pressure of the tubing is equal to or less than ambient. In this state, the pump is unable to generate negative pressures. Upon fluid being supplied to the tubing at a pressure greater than ambient, the tubing inflates and cooperates with rollers of the pump to transmit the fluid. The pump also includes a novel means for adjusting and regulating the tension of the tubing further enhancing the operating life of the tubing.

STATEMENT OF GOVERNMENTAL SUPPORT

This invention was made with support from the U.S. Government underGrant No. 5 R01 HD15434 awarded by the National Institute of Health. TheU.S. Government has certain rights in this invention.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.776,091, filed Oct. 11, 1991, now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to pumps and particularly to peristalticpumps in which a fluid is forced through a tube by progressivelycompressing the tube at spaced apart intervals. Pumps of this generaltype have found particular utility in the medical field for transferringblood and other fluids between a patient and an extracorporeal device.

While a variety of pumps have been previously used, pumps used inconnection with extracorporeal circulation are most commonly of theperistaltic type. Medical procedures which commonly employ peristalticpumps include open heart surgery for circulating blood between a patientand a heart lung machine, dialysis procedures for transferring bloodbetween a patient and a dialyzer, and continuous care situations for thepumping of intravenous solutions.

Peristaltic pumps are volumetric pumps in which a linearly moving orrotating member progressively compresses a flexible tube at spaced apartintervals to propel a fluid through the tube. A principal advantage ofthe peristaltic pump is its simplicity of operation and the absence ofcontact between the fluid, such as blood, and frictional surfaces, suchas internal valves, which can be responsible for a variety of hazards.Instead of directly contacting the rotating member of the pump, thefluid is passed through a chemically inert tube.

Pumps of this type exhibit certain disadvantages which are inherent inthe pumps themselves. Current roller pumps, often used for pumpingblood, are typically driven by a constant speed motor which draws bloodat a substantially constant rate. If a line downstream of the pumpbecomes occluded, the pump can over pressurize and rupture thedownstream vessel. If a line upstream of the pump becomes occluded, thepump can generate dangerously low negative pressures, hemolyze theblood, and empty the tissue vessel of the patient causing a collapse ofthe vessel and resulting in damage to the tissue at the drainagecatheter tip. Roller pumps in general are also inefficient in thisoperation. Much of the energy which is consumed by the pump is used todeform the thick walls of the flexible tubing, an action which in and ofitself does not contribute to output flow. Furthermore, during long termuse with a patient, the tubing presently employed with standard rollerpumps requires being "walked" or replaced because of the wear induced bythe cyclic application of high bending stresses as the rollers occludethe tube.

Pumps can be found in the prior art with regulating devices to controlthe available pumping volume of the pump. For example, in oneperistaltic pump, described in U.S. Pat. No. 3,784,323, the material andthickness of the tube is selected to that there is a predetermineddifferential pressure between the exterior and interior of the tube.Collapse of the tube wall, limiting the flow rate of blood through thetube, occurs as a function of the pump inlet pressure. Thus, the flowrate through the pump will lessen and the tube will become restricted ifthe supply of blood decreases. This prevents a collapse of the tissuevessel and possible damage thereto. However, the restricted tubing isonly partially collapsed and allows the pump to produce very highnegative pressures. Furthermore, when in its collapsed state, highbending stress are induced in the crimped edges of the tubing resultingin a limited useful life.

In another peristaltic pump as described in U.S. Pat. No. 4,515,589, thepump is provided with a pumping element comprised of an outer tubing andan inner tubing. An annular air space, maintained between the inner andouter tubing, is vented to atmosphere. When the hydrostatic head of ablood reservoir is maintained above a given pump head level, the innertubing will expand and fill with blood. When the reservoir level ofblood drops below the pump head level, the inner tube collapses and thepump output stops. However, on "full" collapse of the inner tubing, twopassageways remain open as the cross-section of the inner tube assumes adumbbell or ∞ (infinity symbol) configuration. The inner tube istherefore not "completely" collapsed. Also, the inner tubing repeatedlyexperiences high bending stresses at its edges as it becomes occluded,both during forced collapse caused by the rollers and during collapse asa result of a loss of pressure, which leads to fatigue and wear in thetubing.

With the above described prior art in mind, it is an object of thisinvention to provide for an improved peristaltic pump having inherentpressure regulation and in which, the output flow is dependent upon theinlet supply. A peristaltic pump according to this invention exhibitslow hemolysis and does not generate negative pressures.

A further object of this invention is to provide for a peristaltic pumpwhich exhibits an increased pumping efficiency and which has increaseddurability permitting use in long term support situations.

In achieving the above objects, the present invention utilizes acombination of features and provides for a peristaltic pump in which aflexible tubing is acted upon by rollers which progressively compressthe tubing at spaced apart locations. The tubing itself is of a shapewhich is naturally flat and occluded when the pressure within the tubingis equal to or less than ambient pressures. The tubing is positioned inthe peristaltic pump such that a flat side of the occluded tube is laidflat along the width of the rollers with the edges of the tubing awayfrom the center of the rollers.

As the rollers are rotated, a peristaltic motion is imparted to thetubing. This motion in turn drives the blood from the inlet of the pumpto its outlet. During operation, blood is supplied to the inlet at apressure above ambient, the tubing fills and inflates, and theprogressive compression of the tubing produces the pumping action. Ifthe supply of blood to the pump is discontinued, blood will be pumpedout of the tubing as the tubing completely flattens back into itsnatural or free condition. Being completely flat and occluded when noblood is being supplied to the pump, no negative pressures are generatedwithin the tubing by the rollers.

Additionally, the novel shape of the tubing in the present inventionallows the tubing to assume its completely occluded position withoutinducing high bending stresses along the edges of the tubing. Thisdesign therefore minimizes wear and fatigue and increases the durabilityof the tubing enabling and enhancing use in long term use situations.

The peristaltic pump of the present invention also includes a means forcontrolling the pressure which can be generated within the tubing. Inthis regard, the pump is provided with a mechanism which varies thetension of the tubing. The tensioning mechanism simultaneously adjuststhe positions of both the inlet and outlet ends of the tubing therebyreducing the distance previously required for the same amount of tensionadjustment. The tensioning mechanism also "absorbs" or countersdisplacement of the tubing caused by the changing position of therollers and thus allows for a flexible but inelastic tubing to be used.

One embodiment of a generally inelastic tubing is disclosed. In theembodiment, the tubing is reinforced with a fabric mesh thatsubstantially prevents elongation of the tubing under tension.

An adjustable occlusion block is provided with the pump to permitaccurate control of the outlet pressure as a roller disengages from thetubing adjacent to the outlet of the pump.

Additional benefits and advantages of the present invention will becomeapparent to those skilled in the art to which this invention relatesfrom the subsequent description of the preferred embodiments and theappended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a peristaltic pump incorporatingthe principals of the present invention;

FIG. 2 is a side elevation view of the peristaltic pump illustrated inFIG. 1;

FIG. 3 is a cross-sectional view taken substantially along line 3--3 inFIG. 1 illustrating the tubing in its inflated condition:

FIG. 4 is a simplified front view of a peristaltic pump incorporatingthe principles of the present invention when the supply of pumping fluidhas been discontinued;

FIG. 5 is a cross-sectional view taken substantially along line 5--5 inFIG. 4 illustrating the tubing in its naturally occluded condition;

FIG. 6 is an exploded view of a second embodiment of the tubing utilizedin the present invention which features two sheets of material beingbonded together along their longitudinal edges;

FIG. 7 is a perspective view of a second embodiment of the tubing;

FIG. 8 is a cross-sectional view taken substantially along line 8--8 inFIG. 7 of the tubing in its occluded condition;

FIG. 9 is a cross-sectional view illustrating the second embodiment ofthe tubing in its inflated condition; and

FIG. 10 is a simplified front view of another embodiment of theperistaltic pump of the present invention in which the tension of thetubing is controlled and adjusted through a pivoting mounting plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now with reference to the drawings, a peristaltic pump used for pumpingfluid, such as blood, from a patient to an extracorporeal device (notshown) and back to the patient, is illustrated in FIG. 1 and generallydesignated at 20. It is anticipated that the pump 20 of the presentinvention will have utility in a variety of extracorporeal applicationsincluding, but not limited to, cardiopulmonary bypass, bloodoxygenation, carbon dioxide removal, hemodialysis, blood filtration andother medical procedures.

Generally, the pump 20 is comprised of a frame 22 which includes a wheelor rotor 24. The rotor 24 is mounted to the frame 22 for rotation aboutan axis defined by a shaft 26 centrally disposed therein. The shaft 26is driven by an electric motor or other suitable driving means whichcauses the rotor 24 to rotate, indicated as being clockwise by arrow 30in FIG. 1.

The rotor 24 itself includes a pair of plates, hereinafter designated asthe interior plate 32 and the exterior plate 34, between which aremounted a plurality of rollers 36. (For the sake of clarity indescribing the underlying structures, the pump 20 is illustrated in FIG.1 with the exterior plate 34 removed.) The rollers 36 are axiallyaligned with the shaft 26 and are radially displaced around the rotor 24at equal distances. In this manner, as the rotor 24 is rotated by themotor 28, the rollers 36 will move in a circular path. In theillustrated embodiment, three rollers 36 are shown as being spacedapproximately 120° apart. As the skilled artisan will appreciate, thenumber of rollers utilized will depend on the specific application andthe rotor 24 can be designed to carry the rollers 36 in a non-circularpath.

Each roller 36 is mounted in the rotor 24 so as to be rotatable about anaxis extending therethrough parallel to the shaft 26. For reasons morefully described below, the rotational mounting allows the rollers 36 tomove along a flexible conduit or tubing 38 without a significant amountof frictional pull on the tubing 38.

The flexible tubing 38 is positioned around the array of rollers 36 andsecured by an attachment means, generally designated at 40 and furtherdescribed below, which secures both an inlet end 42 and an outlet end 44of the flexible tubing 38. The tubing 38 forms the pumping chamber ofthe pump 20.

As seen in FIGS. 4 and 5, the tubing 38 is naturally flat when no bloodis being supplied to the pump 20 and when the pressure within thepumping chamber is equal to ambient. The naturally flat shape of theflexible tube 38 is hereinafter referred to as the "free" condition andis generally designated at 46. The flexible tubing 38 is positionedaround the rollers 36 in a manner which places the flat sides 47,exhibited by the tubing 38 in its free condition 46, in surface tosurface contact with the circumferential surface of the rollers 36.Thus, the edges 48 of the tubing 38, in its free condition 46, arelongitudinally spaced along the rotational axes of the rollers 36.

As the rotor 24 rotates the rollers 36, a peristaltic movement isimparted to the flexible tubing 38. With blood being supplied to theinlet end 42 of the flexible tubing 38 at a pressure above ambient, thetubing 38 inflates to the shape generally shown in FIG. 3. Thiscondition is hereafter referred to as inflated condition 50.

Blood is received into the inlet end 42, as shown by arrow 52, from asupply tube 53 and driven through the passageway of the flexible tubing38 until being discharged, as shown by arrow 54, from the outlet end 44to an outlet tube 55 which may route the blood to an extracorporealdevice. If the supply of blood to the pump 20 is discontinued, the bloodcontained within the flexible tubing 38 will be pumped out by therollers 36 and the flexible tubing 38 will collapse into its completelyoccluded free condition 46. Since the flexible tubing 38 is naturallyflat, the tubing exhibits no tendency to return to the inflatedcondition 50 and no negative pressures are generated therein.

In its inflated condition 50, the tubing 38 exhibits what may bereferred to as lemon shape. The sides 47 of the inflated tubing 38 arebellowed outward from the increased internal pressure and converge atoutwardly directed edges 48. Where the sides 47 converge into the edges48, the inner radius of curvature exhibited by the tubing approacheszero. Several methods of construction can be utilized to produce tubing38 having this desired characteristic.

In one method of construction, a thin walled tubing of flexiblematerial, such as vinyl, is heat treated and permanently deformed intothe free condition 46 shape. A tubing constructed by this method isillustrated in the cross-sectional views of FIG. 3 and FIG. 5.

A second method of constructing the flexible tubing 38 utilized with thepresent invention involves adhering two films or sheets of flat,flexible material together along their longitudinal edges to produce aflexible tubing 38 having the desired free condition 46 shape. The edgesof the sheets may be adhered by heat sealing or by the use of adhesives.The cross-sectional area of the passageway through the flexible tubing38 may be constant or may be varied by sealing the edges in a convergingor diverging fashion. The latter method resulting in a reduction in thetotal priming volume required by the pumping chamber.

Generally, the cross-sectional shape of the flexible tubing, andspecifically the interior radius of curvature of the edges 48 whichapproaches zero, reduces the bending stresses applied to the tubing 38during collapsing of the inflated tubing 38 as caused by the rollers 36or a reduced inlet pressure. With bending stresses reduced, tubing wearand fatigue is minimized.

As can be seen from the above discussion, tubing 38 must be flexible.However, depending on the actual material used, the material itself mayrequire that the tubing be elastic or inelastic. For example, whensilicone (an elastic material) is used as the tubing material, theresiliency of the tubing 38 will allow it to stretch and return to itsoriginal length in response to the action of the rollers 36. Silicone,unfortunately, is known to exhibit less than ideal wear characteristics.In another example, when vinyl, exhibiting improved wear characteristicsover silicone, is used as the tubing material, once stretched by theaction of the rollers 36 it remains stretched.

Fortunately, with the present invention the tubing 38 need not beelastic. A substantially inelastic flexible tubing, hereinafterdesignated by reference number 38', is illustrated in FIGS. 6 through 9.Generally, the inelastic tubing 38' includes a reinforcement structurewhich provides those structural attributes which resist stretching. Inproducing the inelastic tubing 38', a mesh reinforcement 56 which doesnot substantially elongate under tension is embedded within the sheetsof flexible material. The mesh reinforcement 56 may be formed ofpolyester or a similar material. Since the mesh 56 resists elongation,it prevents substantial longitudinal elongation and lateral contractionin the tubing 38' as a result of tension caused by the rollers 36. Ascan be seen from the above discussion, vinyl can be used as the tubing38' material since the vinyl will no longer experience permanentelongation.

The pressure generated within the pumping chamber is controlled by thetension of the tubing 38 around the rollers 36. At higher tension, thetubing 38 becomes increasingly occluded at the locations where engagedby the rollers 36, resulting in a higher pressure being held in thepumping chamber. The tension of the tubing 38 is varied by adjusting thepositions of the inlet and outlet ends 42 and 44 of the tubing 38relative to the rotor 24. In achieving this adjustment, a single elementis coupled to both ends 42 and 44 of the tubing 38 so as to provide forconcurrent and simultaneous adjustment. With a tensioning mechanism ofthis type, the tension of the flexible tubing 38 and the pressureexhibited by the pumping chamber may be quickly adjusted through asingle, yet simultaneous, movement of both ends 42 and 44. (Thismovement being half the distance of that required by a tensioningmechanism operable with only one end of a tubing as seen in prior artdesigns.) Also, to permit use of an inelastic tubing 38', the tensioningmechanism 58 is provided with a means for "absorbing" or countering thedisplacement of the tubing 38 which will be caused by the rollers 36changing position during rotation.

Two embodiments of the tensioning mechanism 58 are disclosed herein. Oneembodiment is illustrated in FIGS. 1, 2, and 4 while another embodimentis generally illustrated in FIG. 10.

In both embodiments, the attachment means 40, typically a clamp or otherwell known mechanism, is coupled to a tension plate 60 to secure theends 42 and 44 of the tubing 38. The attachment means 40 itselfcooperates with the tension plate 60 in a V-shaped portion 62, centrallyformed therein and directly toward the rotor 24, such that the ends 42and 44 of the tubing 38 are secured on opposing legs of the V-shapedportion 62. In using the V-shaped portion 62, the stretch ordisplacement experienced by the tubing 38, because of the rotation ofthe rollers 36, is reduced. The V-shaped portion 62 brings the ends 42and 44 of tubing 38 closer together allowing the tubing 38 to be morefully wrapped around the rollers 36 while allowing the ends 42 and 44 tobe mounted perpendicularly to the attachment means 40 and the tensionplate 60.

Referring now to the embodiment illustrated in FIGS. 1, 2 and 4, thetension plate 60 is supported between two parallel shafts 64 and ismounted for movement relative to the shafts 64. As such, the tensionplate 60 is provided with bearings 66, e.g. roller bearings, which allowfor a sliding of the tension plate 60 along the shafts 64. Screws 68 arethreadably mounted into bores (not shown) of the shafts 64. A spring orbiasing member 70 is positioned between the tension plate 60 andoperable portion of screw 68 and supports the tension plate 60 thereon.By working the screws 68 into the shafts 64, the spring 70 will beraised or lowered causing the tension plate 60 to move relative to theshaft 64 and thereby adjusting the tension of the tubing 38 around therollers 36. Also, as the rotor 24 is rotated, the springs 70 willdeflect with the tension plate 60 to counter the displacement of thetubing 38.

In the second embodiment, generally illustrated in FIG. 10, the tensionplate 60 is mounted at one end 72 to the frame 22 of the pump 20 througha pivotable mounting 74. The opposing or free end 76 of the tensionplate 60 is coupled to an adjustment block 78 by a spring or biasingmember 80. A slider (not shown), mounted within the adjustment block 78,is connected at one end to the spring 80 and at its opposing end to anadjustment screw 82. By moving the slider vertically within theadjustment block 78, as shown by arrow 84, the free end 76 of thetension plate 60 is generally moved along arrow 86 changing the tensionof the tubing 38 over the rollers 36. Similar to that seen in the firstembodiment, the spring 80 will permit and counter movement of thetension plate 60 during displacement of the tubing 38 resulting from thechange in position of the rollers 36 as they are rotated.

An additional feature of the present invention is an adjustableocclusion block 88. The occlusion block 88, generally illustrated inFIG. 1, is positioned adjacent to the outlet end 44 of the flexibletubing 38 and is adjustable there against to allow for greater controlin the occlusion of the tubing 38 as the rollers 36 disengage therefrom.The occlusion block 88 is provided with an adjustment mechanism (notshown) of a type well known which permits the block 88 to be moved andfixedly positioned toward or away from the rotor 24. Occlusion of thetubing 38 is assisted by a curved surface or raceway 90 of the occlusionblock 88. Preferably, the raceway 90 exhibits a radius of curvaturediffering from the circular path followed by the rollers 36 so that amore constant degree of occlusion is maintained as the rollers 36 begindisengagement adjacent to the outlet end 44 of the tubing 38.

While the above description constitutes the preferred embodiments of thepresent invention, it will be appreciated that the invention issusceptible to modification, variation and change without departing fromthe proper scope and fair meaning of the accompanying claims.

We claim:
 1. A peristaltic pump for pumping fluids comprising:a frame; aplurality of rollers; carrier means for carrying said rollers in spacedapart relation along a predetermined path, said carrier means beingmounted to said frame; drive means for driving said carrier means andcausing said rollers to move along said predetermined path; a flexibleconduit having walls, an inlet end, an outlet end and a passageway beingdefined therethrough, said conduit being collapsed and said passagewaybeing occluded in a free condition when pressure in said conduitpassageway is equal to pressure acting on the outside of said walls,said free condition thereby preventing the generation of negativepressures in said conduit, said conduit exhibiting an inflated conditionwhen pressure in said conduit passageway is greater than that acting onthe outside of said walls, said conduit passageway being at leastpartially open in said inflated condition thereby permitting thetransmission of fluid through said passageway; and mounting means formounting said conduit about said rollers whereby said conduit cooperatesalong part of its length with said rollers and whereby said rollers atleast partially collapse said conduit in said inflated condition therebytransmitting fluid through said conduit by peristaltic movement.
 2. Aperistaltic pump as set forth in claim 1 wherein said conduit issubstantially flat in said free condition, said conduit having two sidesconnected along corresponding longitudinal edges and exhibiting aninternal radius of curvature approaching zero therealong.
 3. Aperistaltic pump as set forth in claim 1 wherein said conduit isintegrally formed.
 4. A peristaltic pump as set forth in claim 1 whereinsaid conduit includes first and second sheets of flexible materialhaving corresponding side edges, said side edges being secured togethertherealong to produce a fluid tight seal.
 5. A peristaltic pump as setforth in claim 4 said conduit exhibits an internal radius of curvatureapproaching zero at edges thereof.
 6. A peristaltic pump as set forth inclaim 1 wherein said conduit is elastic.
 7. A peristaltic pump as setforth in claim 1 wherein said conduit is inelastic.
 8. A peristalticpump as set forth in claim 1 wherein said conduit includes reinforcementmeans for inducing inelasticity in said conduit.
 9. A peristaltic pumpas set forth in claim 8 wherein said reinforcement means is an inelasticmesh.
 10. A peristaltic pump as set forth in claim 9 wherein saidinelastic mesh is embedded in said walls of said conduit.
 11. Aperistaltic pump as set forth in claim 1 further comprising occlusionmeans for adjustably cooperating with said rollers for at leastpartially collapsing said conduit when in said pressurized condition.12. A peristaltic pump as set forth in claim 11 wherein said occlusionmeans is positioned adjacent said outlet end of said conduit.
 13. Aperistaltic pump as set forth in claim 12 wherein said occlusion meanscooperates with said rollers along less than half of the length of saidconduit.
 14. A peristaltic pump as set forth in claim 1 wherein saidadjustable mounting means is adjustable for controlling the tensionexhibited by said conduit about said rollers and controlling the degreeto which said rollers collapse said conduit to thereby determine themaximum pressure generated within said peristaltic pump.
 15. Aperistaltic pump for use with an extracorporeal device, said peristalticpump comprising:a frame; a rotor supported on said frame for rotationabout a first axis, said rotor including a plurality of rotatablerollers being mounted radially from said first axis and being carried bysaid rotor in a generally circular path about said first axis as saidrotor is rotated; drive means being coupled to said rotor for rotatingsaid rotor; a flexible tubing having inlet and outlet ends and having apassageway defined therethrough for transmitting a fluid, said tubingbeing positioned about said rollers and in a free condition whenpressure in said tubing passageway is equal to pressure acting on theoutside of said tubing, said tubing being collapsed and said passagewaybeing occluded, said tubing being inflatable upon the supplying of fluidto said tubing passageway at a pressure greater than pressure acting onthe outside of said tubing, when inflated said tubing cooperating alonga part of its length with said rollers whereby said rollers at leastpartially collapse said tubing thereby transmitting said fluid byperistaltic movement therethrough; and means for adjustably mountingsaid tubing about said rollers, said mounting means including a body towhich said inlet and outlet ends are secured, said body being adjustablein position to vary the tension exhibited by said tubing in cooperatingwith said rollers.
 16. A peristaltic pump as set forth in claim 15wherein said tubing is integrally formed.
 17. A peristaltic pump as setforth in claim 15 wherein said tubing includes first and second sheetsof flexible material having corresponding side edges, said side edgesbeing secured together therealong to produce a fluid tight seal.
 18. Aperistaltic pump as set forth in claim 15 wherein said tubing isinelastic.
 19. A peristaltic pump as set forth in claim 15 wherein saidtubing includes reinforcement means for inducing inelasticity thereto.20. A peristaltic pump as set forth in claim 15 further comprisingocclusion means cooperating with said rollers for at least partiallycollapsing said tubing between said rollers and said occlusion meanswhen said tubing is inflated.
 21. A peristaltic pump as set forth inclaim 20 wherein said occlusion means is adjustable to vary the degreeto which said tubing is collapsed between said rollers and saidocclusion means when said tubing is inflated.
 22. A peristaltic pump asset forth in claim 15 wherein said mounting means simultaneously adjustssaid inlet and outlet ends relative to said rotor to vary the tensionexhibited by said tubing.
 23. A peristaltic pump as set forth in claim15 wherein said body includes a generally V-shaped portion, said inletand outlet ends being secured to said V-shaped portion for movementtherewith.
 24. A peristaltic pump as set forth in claim 23 wherein saidV-shaped portion converges in a direction toward said rotor.
 25. Aperistaltic pump as set forth in claim 15 wherein said body includes afirst portion about which said body is pivotably secured.
 26. Aperistaltic pump as set forth in claim 25 wherein said body includes adisplaceable portion in spaced apart relation to said first portion andbeing coupled to a positioning means for setting the position of saiddisplaceable portion relative to said rotor.
 27. A peristaltic pump asset forth in claim 26 wherein said positioning means includes a biasingmember being coupled to said displaceable portion and permittingdisplacement of said displaceable portion during movement of said tubingas a result of contact with said rollers as said rotor is rotated.
 28. Aperistaltic pump as set forth in claim 15 wherein said body includesfirst and second ends being movably mounted on shafts and beingtranslationally moveable relative to said rotor thereby adjusting thetension exhibited by said tubing.
 29. A peristaltic pump as set forth inclaim 28 wherein said shafts include means for positioning said firstand second ends relative thereto, said positioning means including abiasing member permitting limited displacement of said body relative tosaid shafts as said rotor is rotated.